This invention relates generally to electrical connections in boreholes, and more particularly to an improved mechanical and electrical connection in a wireline used in a borehole.
Wirelines having an inner electrical conductor, a coaxial insulation layer, and an outer protective wire covering are in common usage in boreholes for connecting subsurface survey, steering or logging tools, or other subsurface electrical equipment to surface electrical equipment. Such wirelines are generally routed through a pulley or sheave at the upper level of a drilling rig, and then spooled on a reel in the wireline surface unit. From the reel, wiring connects the wireline conductor or conductors to other surface equipment.
In various situations, it becomes necessary to have a means for making a quick mechanical and electrical connection in such a wireline to either connect two wireline segments together or to connect a wireline to one or more items of subsurface equipment. Combined mechanical and electrical connectors for such wirelines in borehole usage are generally referred to as "rope socket assemblies". Such connectors must be easy to make-up to reduce costs, due to lost time; they must be mechanically very strong, providing breaking tensile strengths near or in excess of the wireline itself; and the electrical connection must be well isolated from the drilling medium or other borehole fluid material to prevent shorting of the inner electrical conductor to the outer protective wire covering.
Previous design practices have resulted in rope socket assemblies that are generally large in diameter, compared to the wireline diameter, and quite long. Typical units have been on the order of 1.375 inches in diameter and larger, and 12 or more inches in length, for a typical 5/16 inch diameter wireline, for example. Further, the sealing means to isolate the electrical connection from fluids in the borehole have shown limited reliability; and their size has contributed to the overall size of existing rope socket assemblies.
The large, overall dimensions for existing technology rope socket assemblies have made it impossible to route such assemblies through the pulley or sheave at the upper levels of a drill rig, or to retrieve and wind the wireline onto the reel in the wireline surface unit. These restrictions often require the cutting or mechanical removal of such rope socket assembly components from the wireline each time the wireline must be retrieved from the borehole. This requirement leads to increased costs of operation, not only upon the retrieval of a wireline, but also upon the reinsertion of the wireline into the borehole, since the connections must be remade as the wireline is traversed into the borehole. Accordingly, there is great need for improved apparatus obviating the above difficulties and restrictions.